1,2

When the size of the row is odd, it is impossible to find such an arrangement, so that sequence is only defined for even-sized rows.

Table of n, a(n) for n=1..8.

a(1) = 1, because of [1, 2].

a(2) = 2, because of [1, 2, 3, 4] and [1, 4, 3, 2].

a(3) = 2, because of [1, 4, 3, 2, 5, 6] and [1, 6, 5, 2, 3, 4].

Cf. A036440.

Sequence in context: A067700 A270554 A037010 * A114695 A134084 A267346

Adjacent sequences: A294181 A294182 A294183 * A294185 A294186 A294187

nonn,more

Michel Marcus, Feb 11 2018

approved